pinctrl: ocelot: Fix GPIO interrupt decoding on Jaguar2

pinctrl: ocelot: Fix GPIO interrupt decoding on Jaguar2

This fixes a problem with using the GPIO as an interrupt on Jaguar2
(and similar), as the register layout of the platforms with 64 GPIO's
are pairwise, such that the original offset must be multiplied with
the platform stride.

Fixes: 1ad2d4169ae7 pinctrl: ocelot: add MSCC Jaguar2 support.
Reviewed-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Lars Povlsen <lars.povlsen@microchip.com>
Link: https://lore.kernel.org/r/20200513125532.24585-4-lars.povlsen@microchip.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>